Different types of dental plaque predispose to either caries or periodontal disease. Bacteria are intimately involved in both processes. Their role may be simply overgrowth in areas where hygiene cannot be maintained or certain bacteria may be etiologically responsible. The present proposal will examine both hypotheses as plaque will be removed from non-disease associated sites, and from caries associated sites. Pooling of plaque samples will be avoided so that the bacteriological and biochemical information obtained can be correlated with te clinical appearance of the sampled site. The plaques will be 1) examined bateriologically either by screening for certain bacteria or by partially characterizing the predominant culturable isolates; 2) compared in their physiologic response to certain radioactive nutrients such as sucrose and glucose; 3) genotypes of S. mutans will be compared for carbohydrate metabolisms under varying conditions of pH, osmotic pressure and fluoride concentration.